Flute sealing method

ABSTRACT

A closed edge corrugated core paperboard in which the corrugated core of the board is closed by slitting and compressing the corrugated core edge and by folding the edges of the facing sheets, left projecting after the core is crushed, one folded extending edge folded over the other folded extending edge, and adhesively securing the folded edges together; the method for producing such board including the steps of slitting and crushing the end of the core, folding the edges of the facing sheets, one over the other, and adhesively securing the folded edges of the facing sheets to each other; and, the apparatus for producing such board and for carrying out such method, which apparatus includes rotating slitter knives for slitting the end of the corrugated core, means for compressing the slit end and means for folding the extending facing sheet edges, one over the other, and for adhesively securing the folded edges to each other.

Umted States Patent 1191 1111 3,711,352 Wagers et a1. 1 1 Jan. 16, 1973 54 FLUTE SEALING METHOD 2,293,751 8/1942 May ..l56/2l1 [75] Inventors: William wagers Smithvme; 3,031,356 4/1962 Bousouet et al... .....156/202 3,307,995 3/1967 Martin ..l56/216 Robert H. Frappier, Wooster, both 3 553 048 l 1971 R 56 216 of Ohio- William s. McDonald l 7 3,579,396 5/1971 Washburn et a1. ..156/202 Assignee:

Filed:

Georgetown, S.C. Charles L. Boggs, Statesville, NC.

International Paper Company, New

York, NY.

Sept. 14, 1970 Appl. No.: 71,865

Related U.S. Application Data Division of Ser. No. 721,739, April 16, 1968, Pat. No. 3,563,843.

' Att0meyChar1es B. Smith [57] ABSTRACT A closed edge corrugated core paperboard in which the corrugated core of the board is closed by slitting and compressing the corrugated core edge and by folding the edges of the facing sheets, left projecting after the core is crushed, one folded extending edge folded over the other folded extending edge, and adhesively securing the folded edges together; the method for producing such board including the steps of slitting and crushing the end of the core, folding the edges of the facing sheets, one over the other, and adhesively securing the folded edges of the facing sheets to each other; and, the apparatus for producing such board and for carrying out such method, which apparatus includes rotating slitter knives for slitting the end of the corrugated core, means for compressing the slit end and means for folding the extending facing sheet edges, one over the other, and for adhesively securing the folded edges to each other.

3 Claims, 28 Drawing Figures PATENTEDJAN 16 I975 SHEET 4 UF 8 PATENTEDJAH 1 6 I975 3.711.352

saw e [If 8 IIII) PATENTEDJAH 16 1915 3,71 1. 352

SHEET 7 or 8 3m wmm Sm .Km .Km 9% ya, am gm 8% Wm r V 9mm ymmm m Rm m mmm W i f g v mww mm @mm m \RWW bunk \Qwmx A QQM amum m aw. gm mwx PATENTEDJAR 16 I975 SHEET 8 [IF 8 m mm EWKVMV o w m Nu F w ll m IS mm FLUTE SEALING METHOD CROSS REFERENCE TO RELATED APPLICATION This application is a divisional application of application Ser. No. 721,739, filed Apr. 16, 1968, in the name of the present inventors, now U.S. Pat. No. 3,563,843.

This invention relates to corrugated core paperboard and, more particularly, to methods and apparatus for forming an end closure over one or more of the open, or fluted, edges of the corrugated core by folding and adhesively securing extending portions of the facing sheets at the edge of the board over the open, or fluted edge, of the corrugated core and to the closed edge corrugated core paperboard formed thereby.

Corrugated core paperboard, formed from a corrugated paper core with facing sheets secured to the opposite faces thereof, is used for many purposes including containers. In such board, the convolutions of the corrugated core space the facing sheets and, at the opposite edges of the board, the convolutions, or flutes, are open. Thus, there is a space between the sheets at the opposite edges of the board into which dirt, foreign matter or the material packaged in the container, can flow. Furthermore, such edges are relatively weak, are easily crushed and, along such edges, the paperboard is relatively flexible.

Various attempts have, heretofore, being made to close the open, or fluted, ends of corrugated paperboard to prevent dirt, foreign matter, and the like, from entering the space between the facing sheets and to stiffen and reinforce the edge. In one such arrangement, one of the facing sheets is extended beyond the edge of the corrugated core and the other facing sheets and is folded over the open, or fluted edge of the corrugated core and adhesively secured to the outer face of the other facing sheet. While such edge wrapping does close the open end of the core, wrapping of the edge in this manner increases the thickness of the board at the wrapped edge. Furthermore, in so wrapping the edge, the corrugated core is easily crushed or damaged, detracting from the appearance and weakening the board The corrugated core paperboard produced by the methods and apparatus of the instant invention has a square edge formed by slitting and compressing the edge of the corrugated core and by folding the extending edges of the facing sheets over the compressed edge of the core. The folded edge of one of the facing sheets is folded over the compressed edge of the core, an adhesive is applied, and the edge of the other facing sheet is folded over the folded portion of the first facing sheet and adhesively secured thereto.

The edge thus formed is square, made up of the folded portions of the two facing sheets, one over the other, adhesively secured together. The thickness of the board, at the edge, is not increased and the edge is stiffened, or reinforced, by the overlapping and adhesively secured portions of the facing sheets.

In the method and apparatus of the instant invention, the corrugated core, intermediate the facing sheets, is slit, or cut, along the paperboard edge substantially parallel to the planes of the facing sheets. The slit edge of the corrugated core is then compressed, or crushed, inwardly between the facing sheets, leaving the edges of the opposed facing sheets extending outwardly beyond the crushed edge of the corrugated paper core.

The extending edges of the facing sheets are folded over the compressed, or crushed, edge of the corrugated core, an adhesive is applied and the extending edges of the facing sheets are adhesively secured together along the edge of the board, closing and reinforcing the edgesf The apparatus in the instant invention includes a belt arrangement for contacting the top and bottom facing sheets of the corrugated core paperboard and for feeding the corrugated core paperboard along a pre-set path. As the board moves along the path, the edge of the corrugated core to be closed, is fed past a slitting roll which cuts, or slits, the edge of the corrugated core. The slit edge is then fed past a compressing roll which compresses, or crushes, the slit edge of the core leaving theedge portion of the facing sheets projecting and then fed past a series of guides which first fold the extending edge of one of the facing sheets into contact with the compressed, or crushed, core edge and then fold the extending edge of the other facing sheet into contact with the folded portion of the first facing sheet. The last folded extension is unfolded, an adhesive is applied and the unfolded extension is refolded and held in contact with the first folded extension until the adhesive dries, sets or hardens.

In the following description of the preferred embodiment and the appended drawings.

FIG. 1 is a perspective view showing the corrugated core paperboard of the instant invention with a portion of the corrugated core edge cut or slit and a portion of the slit edge compressed or crushed;

FIG. 2 is a view similar to FIG. I but showing one of the facing sheet edges folded over the slit and compressed corrugated edge and the other facing sheet edge projecting therebeyond;

FIG. 3 is a view similar to FIG. 2 showing both facing sheet edges folded over the slit and compressed corrugated edge;

FIG. 4 is a view similar to FIG. 3 showing one of the folded facing sheet edges unfolded to receive an adhesive.

FIG. 5 is a view similar to FIG. 4 showing the adhesive applied;

FIG. 6 is a view similar to FIG. 5 showing both facing sheet edges folded and adhesively secured;

FIG. 7 is a side elevation view showing, at the left hand end of the drawing, the apparatus of the instant invention and, at the right hand end, the feed table associated therewith;

- FIG. 8 is a top plan view of the apparatus of FIG. 7 showing, in full and dotted lines, various adjustments of the apparatus;

FIG. 9 is a vertical cross sectional view taken along line 9-9, FIG. 7;

FIG. 10 is a view similar to FIG. 9 but taken along line l0-l0, FIG. 7;

FIG. 11 is a fragmentary enlarged sectional view, in side elevation, taken along line 11-11, FIG. 9;

FIG. 12 is an enlarged sectional view, in end elevation, taken along line l2l2, FIG. 11;

FIG. 13 is a vertical section taken along line 13-13, FIG. 9;

FIG. 14 is an enlarged fragmentary plan view of a part of the apparatus of FIG. 8;

FIG. is a side view, partly in section, of the apparatus of FIG. 14 taken from the back along line 15- 15, FIG. 14;

FIG. 16 is a side view similar to FIG. 15 but taken from the front of the mechanism on the other side of the machine from that of FIG. 14;

FIG. 17 is a view along the side edge of the corrugated core paperboard of the instant invention showing the edge at various states of its formation; and,

FIGS. 18 to 28 are cross-sectional views taken on correspondingly numbered lines on FIG. 17 of the paperboard and the various edge forming units showing the board and the units at the various stages of edge formation.

Referring to FIGS. 1 to 6, the corrugated paperboard includes paper facing sheets 2, 4, adhesively secured to the opposite sides of corrugated core 6, in the customary 'manner, on a conventional corrugated paperboard machine. The edge, or edges, of the board to be closed are trimmed, if necessary, so that, at such edges, the ends of core 6 and facing sheets 2, 4 are flush or in alignment with each other. At the edge to be closed, end of core 6 is cut longitudinally of the board, along a line between facing sheets 2, 4 to a depth substantially equal to the distance between facing sheets 2, 4. The cut edge of core 6 is then crushed, or compressed inwardly, to a depth substantially equal to the distance between facing sheets 2, 4.

In compressing the cut edge of core 6 inwardly, corrugated core 6 is substantially stripped off of the inner surface of facing sheet 2, 4, without bending or damaging facing sheets but, rather, leaving the facing sheets intact and extending outwardly, at the crushed corrugated core edge, a distance substantially equal to the distance between facing sheets 2, 4. One of the facing sheets is folded over the crushed end of core 6 so that the folded portion of the facing sheet is substantially at right angle, or normal, to the plane of the facing sheet with its edge near or in contact with the inner surface of the other sheet. The extending edge of the other sheet is folded over the folded edge of the first sheet, unfolded, adhesive is applied and the edge is refolded into engagement with the folded edge of the first sheet and held in position until the adhesive dries, sets, or hardens.

As illustrated in FIGS. 1 to 6, the edge of corrugated core 6 is cut at 60 and compressed or crushed leaving edge portions 2a and 4a extending outwardly from facing sheets 2, 4, respectively, beyond the crushed edge of core 6. Edge 2a is folded downwardly, substantially perpendicular to facing sheet 2, into substantial contact with the upwardly facing surface of facing sheet 4. The extending edge 40 of facing sheet 4 is folded upwardly into engagement with folded edge portion 2a of sheet 2. Edge 4a is then unfolded downwardly and adhesive 8 (FIG. 5) is applied to edge portion 4a and edge portion 4a is refolded upwardly and held in contact with folded edge portion 2a until adhesive 8 dries, sets or hardens.

As best shown in FIG. 6, the open or fluted edge of the board is closed by the folded over edges 2a, 4a of facing sheets 2, 4, and folded over edges 2a, 40 because folded, one over the other, and adhesively secured together, form a 2-ply, square edge over the fluted end of the core, closing, stiffening and reinforcing the edge of the board.

One or both of the open edges of the corrugated paperboard are closed, in the instant invention, by feeding a sheet of corrugated paperboard along a path in a direction transverse to the direction of the convolutions of the corrugated core. As the board is fed along the path, the corrugated edge to be closed is slit intermediate the facing sheets, the slit edge of the core is compressed or crushed, and the edges of the facing sheet are folded over the edge of the core and adhesively secured.

Referring to FIGS. 7 to 28, the apparatus of the instant invention includes a table, generally designated 10, having a top 12 with guides 14, 16 and a roller 18 mounted on arms 20, 22 and extending outwardly from table 10 in substantial alignment with top 12. A frame, generally designated 24, is attached at 26, 28 to the end of table 10, at the end of the table opposite roller 18. Supports 30, 32, 34, 36 extend upwardly from the four corners of frame 24.

Shafts 40, 42, are mounted at their opposite ends in bearings 44, 46, 48, 50, fixed to supports 30, 32 and, intermediate their ends, are threaded at 49, 51 (FIG. 9), for purposes hereinafter described. Sprocket 52 and crank handle 54 are keyed to one end of shaft 40 and sprockets 56, 58 are keyed to the end of shaft 42.

Shafts 60, 62 (FIGS. 7, 8 and 10) are mounted, at their opposite ends, in bearings 64, 66, 68, 70, fixed to supports 34, 36, and are threaded intermediate their ends, at 70, 72, for purposes later described. Sprocket 74 is keyed to the end of shaft and sprockets 76, 78, are keyed to the end of shaft 62. Sprockets 52 and 58 are interconnected by chain and sprockets 74, 76 are interconnected by chain 82. Sprockets 56 and 78 are interconnected by chain 84. Thus, by turning crank 54, shafts 40, 42, 60, 62 are rotated in their respective bearings in supports 30, 32, 34, 36 for purposes hereinafter described.

As best shown in FIG. 9, shaft having a longitudinal extending keyway 91, and shaft 92 having a longitudinal extending keyway 93, are mounted at their opposite ends for rotation in bearing 94, 96 and 98, 100, fixed to supports 30, 32. Sprocket 102 is keyed to shaft 90 and sprockets 104, 106 are keyed to shaft 92. Sprockets 102, 104 are connected by chain 108 and chain 108 passes around idler sprocket 110 mounted on a cross member of frame 24 (FIGS. 9, 13). Sprocket 106 is connected by chain 112 to variable speed drive 114 driven by motor 116 (FIG. 7). Belt rolls 118, 120, are keyed to shaft 90 in longitudinal keyway 91 and belt rolls 122, 124, are keyed to shaft 92 in longitudinal keyway 93. Belt roll 118 is held in fixed position longitudinal of shaft 90, for rotation with shaft 90, by thrust bearings 126, 128, mounted in plates 130, 132, fixed by, for example, welding, to block 134 carried, by bearings 136, 138, and collars 140, 142, fixed by set screws 141, 143, respectively, on shaft 40. For reasons hereinafter apparent, shaft 40 is rotatable in block 134.

Belt roll 120 is held in fixed position longitudinal of shaft 90, for rotation with shaft 90, by thrust bearings 144, 146, mounted in plates 148, 150, fixed by, for example, welding, to block 152, threaded onto threads 49 to shaft 40.

Belt roll 122 is held in fixed position longitudinally of shaft 92, for rotation with shaft 92, by thrust bearings 154, 156, mounted in plates 158, 160, fixed by, for example, welding, to block 162 carried by bearings 164, 166, and collars 168, 170, set on shaft 42. Belt roll 124 is held in fixed longitudinal position on shaft 92, for rotation with shaft 92, by thrust bearings 172, 174 mounted in plates 176, 178, fixed by, for example, welding, to block 180 threaded onto threads 51 of shaft Plates 130, 132, 148, 150, 158, 160, 176, 178, extend longitudinally of frame 24 and, as best shown in FIG. 10, support, at the opposite end of frame 24, belt rolls 180, 182, 184, 186. Belt roll 180 is rotatably supported in plates 130, 132 fixed by, for example, welding, to block 186 carried by bearings 188, 190, and collars 192, 194, set to shaft 60. An extension 187 on block 186 extends outwardly from block 186 around upper cross head 189 fixed, at its opposite ends, to supports 34, 36, and is adjustable thereon by said screw 191. Belt roll 182 is rotatably supported in plates 148, 150, fixed by, for example, welding, to block 192 threaded onto threads 70 of shaft 60. An extension 193 of block 192 extends upward around upper cross head 189 and is supported thereon by roller 195.

Belt roll 184 is mounted for rotation on plates 158, 160 fixed by, for example, welding, to block 196 mounted by bearings 198, 200, and collars 202, 204, set to shaft 62. The lower end of block 196 rests on lower cross head 206 of frame 24 attached at its opposite ends to supports 34, 36.

Belt roll 186 is mounted for rotation on plates 176, 178, fixed by, for example, welding, to block 208 threaded onto threads 72 of shaft 62. Roller 210, mounted for rotation on a downward extension of block 208, is in rolling contact with the upper surface of lower cross head 206 of frame 24.

Endless belt 212 extends around belt rolls 120, 182, and endless belt 214 extends around rolls 124, 186. Similarly, endless belt 216 extends around belt rolls 118, 180, and endless belt 218 around belt rolls 122, 184. Each of the endless belts 212, 214, 216, 218, has a roughened outer surface to grip and feed a corrugated paperboard sheet between belts 216, 218, and the belts are spaced to grip and feed the corrugated paperboard sheet without crushing, damaging or marring the faces of the corrugated sheet.

As has been described, by turning crank 54, shafts 40, 42, 60, 62 are rotated in their respective bearings in supports 30, 32, 34, 36. As crank 54 is turned, shafts 40, 42, 60, 62 rotate in bearings of blocks 134, 162, 186, 196 and the position of these blocks, their connected plates, belt rolls, belts and apparatus thereon remains in fixed position relative to supports 30, 32, 34, 36. Because blocks 152, 180, 192, 206, are connected to shafts 40, 42, 60, 62, by threads 49, 51, 70, 72, as shafts 40, 42, 60, 62 are rotated by turning crank 54, blocks 152, 180, 192, 206 and their connected plates, belt rolls, belts and apparatus thereon are moved axially along shafts 40, 42, 60, 62 toward, or away from, supports 30, 34, depending upon the direction of rotation of crank 54, for reasons hereinafter more apparent.

In the embodiment of the invention illustrated and described, the open, or fluted edges of the core at the opposite edges of the board are cut, crushed and the extending portions of the facing sheets are folded and adhesively secured simultaneously. This is accomplished by various components located along the opposite edges of the corrugated paperboard feed path as the paper is fed by and between belts 212, 214, 216, 218. Such components are mounted on plates 150, 178, and 130, 158 and are moveable therewith. Because the components on the respective plates are identical, the components attached to plates 150, 178 will be described, it being understood, however, that in the described embodiment such apparatus is duplicated on plates 130, 158.

Referring now to FIGS. 11 and 12, plates 148,

are held in parallel fixed position by spacers 220, 222,

224 attached, at their opposite ends, to plates 148, 150 and, similarly, plates 176, 178 are held in fixed parallel position by spacers 226, 228, 230. Rollers 232, rotatably mounted at their opposite ends on plates 148, 150, engage belt 212 and, as a corrugated paperboard sheet is fed by belt 212, hold the belt in engagement with the surface of the paperboard sheet. Rollers 234, 236 are rotatably mounted at their opposite ends on plates 148, 150 and roller 238 is mounted, at its opposite ends, on plates 148, 154 for rotation between the plates and is adjusted on plates 148, 150 by set screw 240 adjustable in block 242 on plate 150. A similar set screw and block are mounted on the outer face of plate 148. By adjustment of the set screws in the blocks, the tension of belt 212 is adjusted.

Rollers 241, rotatably mounted at their opposite ends, on plates 176, 178, engage belt 214 and, as a corrugated paperboard sheet is fed by belt 214, hold belt in engagement with the surface of the paperboard sheet. Rollers 242, 244, are rotatably mounted at their opposite ends on plates 176, 178, and roller 246 is mounted at its opposite ends on plates 176, 178, and is adjustable on plates 176, 178 by set screw 248 adjustable in block 250 on plate 178. A similar set screw and block are mounted on the outer face of plate 176 and, by adjustment of the set screws in the blocks, the tension of belt 214 is adjusted.

Guide plate 252, having slots 254, is adjustably mounted on plate 150 by screws 256 and is adjusted relative to plate 150 by loosening screws 256, sliding plate 252 upwardly or downwardly and retightening the screws. The lower edge of plate 252 is adjusted to engage the surface of the upper facing sheet of a corrugated paper sheet as the sheet is fed between belts 212, 214 during operation of the machine.

Brackets 260, 262 are fastened by screws 264, 266 and 268, 270 to plate 178, plate 272 is fastened to brackets 260, 262 by, for example, welding. Referring to FIGS. 14, 15 and 16, cutter wheel, generally designated 280, having a tapered edge knife blade 282, clamped by screws 284, 286, 288, 290, between opposing discs 292, 294, tapered, respectively, at their opposing edges facing the knife edges at 296, 298, is supported for rotation on plate 272 by bolt 300 and is adjustable on plate 272 by set screw 302. Crusher wheel, generally designated 304, having a blunted edge crusher plate 306, clamped by screws 308, 310, 312, 314, between opposing discs 316, 318, tapered, respectively, at their opposing edges facing the crusher plate at 320, 322, is supported for rotation on plate 272 by bolt 324 and is adjustable on plate 272 by set screw 326.

Upper face guide 328, having a guide surface 330 sloping downwardly in the direction of travel of the corrugated paperboard, is mounted for adjustment in the guide way between flanges 332, 334 of mounting block 336, bolted to plate 272 by bolt 338, and is clamped to block 336 by screws 340, 342 in slots in 328. Mounting block 336, guided by guides 337', 337" is adjusted by set screws 344', 356'. Upper face sheet guide 328 is adjusted by set screw 344. Lower face guide 346, having a guide surface 348, sloping inwardly in the direction of travel of the corrugated paperboard, is adjustably mounted by bolts 349, 350 in the guideway between flanges 352, 354 of block 336 and is adjusted in the flanges by set screw 356. Guide 360, having a guiding surface 362 extending downwardly in the direction of travel of the corrugated paperboard, is adjustably mounted by screws 364, 366 in the guideway between flanges 368, 370 on plate 272 and is adjusted by set screw 372. Glue block 374, connected to glue reservoir, not shown, by flexible tube 376 has, at its lower comer, a glue outlet passage 378 and is adjustably mounted in the guideway between flanges 380, 382 by bolt 384 and is adjusted by set screw 386. Lower face sheet guide 390, having guide surface 392 sloping upwardly in the direction of travel of the corrugated paperboard, is adjustably mounted in the guideways between flanges 394, 396 by bolt 398 and is adjusted by set screw 400.

In the operation of the apparatus of the instant invention, corrugated paperboard, trimmed at its edges so that the edges are substantially square, with the edges of the facing sheets and the open end of the corrugation convolutions substantially flush, is fed through the apparatus in a direction transverse to the direction of the corrugated core convolutions. The board, with its edges trimmed, may be fed as a continuous strip from the end of the corrugated paperboard machine producing such board, may be fed from a roll, or precut sheets may be fed, one after the other, through the apparatus. Before feeding the corrugated paperboard through the apparatus, the width of the machine between the opposed cutting and crushing wheels, edge guides and glue applicators, is adjusted to the width of the corrugated paperboard to be edge closed by adjusting crank 54 and aligning the various wheels, edge folders and glue applicators with the appropriate screws and set screws. Guides 14 and 16 on table are adjusted so that they are in alignment with the cutting, crushing folding and gluing apparatus. With motor running and, through variable speed drive 114, driving belts 212, 214, 216, 218, the belts feed the corrugated paperboard through the machines. Plates 252 are adjusted so that the surface of the upper facing sheet slides along the bottom edge of plate 252.

The corrugated paperboard is fed through the apparatus in the direction of the arrows in FIGS. 8 and 17. As the paperboard is fed through station A, FIG. 17, knifes 282 at the opposite edges of the board, cut the corrugated core 6 intermediate facing sheets, 2, 4 and,

as the cut edge passes blunted edge crushing bladesposite sides of crushing blade 306. As the board leaves crushing blade 306, the projecting edges 20 of facing sheet 2 at the opposite edges of the board engage downwardly sloping guide surfaces 330 and are folded downwardly by guides 328 over the crushed edges of core 6. As best seen in FIG. 22, the face of guide surfaces 328, at 331, bent the outermost end of edge portions 20 inwardly toward the core. At station E, FIGS. 17 and 23, the upwardly sloping guide surfaces 348 of lower face guides 346 fold edge portions 40 of facing sheet 4 upwardly and over the previously downward folded portions 2a. At station F, FIGS. 17 and 24, upper and lower embracing figures 357, 359, engage the upper and lower edges of the board, respectively, to square the edge. At station G, FIGS. 17 and 25, folded portions 44 of facing sheet 4 are unfolded and, at station I-I, FIGS. 17 and 26, an adhesive, preferably a hot melt adhesive is applied to the unfolded face of edge portions 4a where the end of edge portions 2a abuts 40. At station J. FIGS. 17 and 27, edge portions 4a are refolded and at station K, FIGS. 17 and 28 are brought into contact with and held against folded portions 2a, spreading the adhesive between the abutting faces of folded portions 20, 4a and holds the folded portions in contact until the adhesive dries, sets or hardens.

In the foregoing description, the open, or fluted, corrugated edges at both edges of the corrugated paperboard are closed as the board is fed through the machine. If it is desired to close only one edge of the board, plate 252 may be lowered to contact the edge, rather than the facing sheet of the corrugated board. When this is done, the machine width is adjusted by crank 54 to receive the board width. Thus, as the board passes through the apparatus, one edge of the board will slide along the side of plate 252 and remain open, while the opposite edge is being closed.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

l. A method for forming an end closure on a paperboard having a corrugated core and facing sheets secured to the opposite sides of said corrugated core, the steps comprising, slitting the end of said corrugated core inwardly and substantially parallel to said facing sheets, compressing said slit end of said corrugated core inwardly so that, at said slit end, at least one of said facing sheets extends outwardly beyond said core, and folding the extensions of said facing sheet over said compressed end of said corrugated core so that said extensions of said facing sheet is in contact with said compressed end of said corrugated core and in a plane substantially normal to the planes of said facing sheets.

2. A method for forming an end closure on a paperboard having a corrugated core and facing sheets secured to the opposite sides of said corrugated core, the steps comprising, slitting the end of said corrugated core inwardly and substantially parallel to said facing sheets, compressing the slit end of said corrugated core inwardly so that, at said slit end, said facing sheets extend outwardly beyond said core, folding first one, and

then the other, of said extensions of said facing sheets over said compressed end of said corrugated core so that the extension of one of said facing sheets is in contact with the compressed end of said core and the extension of the other of said facing sheets is in contact with and overlapping said folded extension of said one .of said facing sheets, said folded extensions of said facing sheets being in a plane substantially normal to the 

2. A method for forming an end closure on a paperboard having a corrugated core and facing sheets secured to the opposite sides of said corrugated core, the steps comprising, slitting the end of said corrugated core inwardly and substantially parallel to said facing sheets, compressing the slit end of said corrugated core inwardly so that, at said slit end, said facing sheets extend outwardly beyond said core, folding first one, and then the other, of said extensions of said facing sheets over said compressed end of said corrugated core so that the extension of one of said facing sheets is in contact with the compressed end of said core and the extension of the other of said facing sheets is in contact with and overlapping said folded extension of said one of said facing sheets, said folded extensions of said facing sheets being in a plane substantially normal to the planes of said facing sheets.
 3. A method as recited in claim 2 including the further step of applying an adhesive to the outer side of said folded extension of said one of said facing sheets before the extending portion of the other of said facing sheets is folded into contact therewith. 